Today in history: On May 18, 1980, the Mount St. Helens volcano in Washington state erupted, leaving an estimated 57 people dead or missing. Also on this date: In 1863, the Siege of Vicksburg began during the Civil War, ending July 4 with a Union victory. In 1896, the U.S. Supreme Court, in Plessy v. Ferguson, endorsed “separate but equal” racial segregation. (The decision was reversed 58 years later by Brown v. Board of Education of Topeka.) In 1927, in America’s deadliest school attack, part